This invention relates generally to implantable devices, such as expandable intraluminal prosthesis. More particularly, this invention relates to an implantable prosthesis having a plurality of micropatterned microdepots formed in the device to deliver fluid to tissues. Moreover, the present invention relates to a method of fabricating micropatterned microdepots in such a device.
A variety of surgical procedures and medical devices are currently used to relieve intraluminal constrictions caused by disease or tissue trauma. An example of one such procedure is percutaneous transluminal coronary angioplasty (PTCA). PTCA is a catheter-based technique whereby a balloon catheter is inserted into a blocked or narrowed coronary lumen of the patient. Once the balloon is positioned at the blocked lumen or target site, the balloon is inflated causing dilation of the lumen. The catheter is then removed from the target site thereby allowing blood to freely flow through the unrestricted lumen.
Although PTCA and related procedures aid in alleviating intraluminal constrictions, such constrictions or blockages reoccur in many cases. The cause of these recurring obstructions, termed restenosis, is due to the body""s immune system responding to the trauma of the surgical procedure. As a result, the PTCA procedure may need to be repeated to repair the damaged lumen.
Stents or drug therapies, either alone or in combination with the PTCA procedure, are often used to avoid or mitigate the effects of restenosis at the surgical site. In general, stents are small, cylindrical devices whose structure serves to create or maintain an unobstructed opening within a lumen. The stents are typically made of, for example, stainless steel, nitinol, or other materials and are delivered to the target site via a balloon catheter. Although the stents are effective in opening the stenotic lumen, the foreign material and structure of the stents themselves may exacerbate the occurrence of restenosis or thrombosis.
Drugs or similar agents that limit or dissolve plaque and clots are used to reduce, or in some cases eliminate, the incidence of restenosis and thrombosis. The term xe2x80x9cdrug(s),xe2x80x9d as used herein, refers to all therapeutic agents, diagnostic agents/reagents and other similar chemical/biological agents, including combinations thereof, used to treat and/or diagnose restenosis, thrombosis and related conditions. Examples of various drugs or agents commonly used include heparin, hirudin, antithrombogenic agents, steroids, ibuprofen, antimicrobials, antibiotics, tissue plasma activators, monoclonal antibodies, and antifibrosis agents.
Since the drugs are applied systemically to the patient, they are absorbed not only by the tissues at the target site, but by all areas of the body. As such, one drawback associated with the systemic application of drugs is that areas of the body not needing treatment are also affected. To provide more site-specific treatment, stents are frequently used as a means of delivering the drugs exclusively to the target site. The drugs are suspended in a tissue-compatible polymer, such as silicone, polyurethane, polyvinyl alcohol, polyethylene, polyesters, hydrogels, hyaluronate, various copolymers and blended mixtures thereof. The polymer matrix is applied to the surfaces of the stent generally during the manufacture of the stent. By positioning the stent at the target site, the drugs can be applied directly to the area of the lumen requiring therapy or diagnosis.
In addition to the benefit of site-specific treatment, drug-loaded stents also offer long-term treatment and/or diagnostic capabilities. These stents include a biodegradable or absorbable polymer suspension that is saturated with a particular drug. In use, the stent is positioned at the target site and retained at that location either for a predefined period or permanently. The polymer suspension releases the drug into the surrounding tissue at a controlled rate based upon the chemical and/or biological composition of the polymer and drug.
The above-described devices and methods for treatment of restenosis and thrombosis, and other similar conditions not specifically described, offer many advantages to potential users. However, it has been discovered that such devices and methods may be deficient in their current drug-loading and drug-delivery characteristics. In particular, the amount or volume of drug capable of being delivered to the target site may be insufficient due to the limited surface area of the stent.
In view of the above, it is apparent that there is a need to provide a fluid delivery device offering increased drug loading capabilities for stents and other prosthetic devices. It is also desirable that the drug-delivery device allows fluids to be released at variable and/or independent rates. There is also a need to provide a method of manufacturing such an improved fluid delivery device that is convenient, efficient and cost effective.
In accordance with various aspects of the present invention, an implantable prosthesis, one example of which includes a stent, has a body structure that is generally cylindrical in shape with a hollow bore that extends longitudinally through the body structure. The outer surface of the prosthesis is capable of contacting an inner lumen surface of a passageway. In addition, the body structure of the prosthesis has one or more micropatterned microdepots formed therein. The depots have an open end, a closed end, a diameter and a depth that is less than the thickness of the body structure of the prosthesis. In general, the depots have an inverted-conical shape, whereby the diameter of the depots decreases from the closed end to the open end of the depots.
Another aspect of the present invention is a method of forming pores on an implantable prosthesis. The method is applicable not only to the above-described prosthesis, but also to any implantable prosthesis having a surface. The method includes applying a first fluid onto the surface of the prosthesis, the first fluid forms a protective coating on the surface. A mask having transparent and opaque area is generated. In general, the transparent areas represent the pores that are to be applied to the prosthesis. The mask is illuminated with light so that the light passes through the transparent areas forming exposed metal areas on the surface of the prosthesis. A second fluid that dissolves the exposed metal areas to a predetermined depth, thereby forming a well, is also applied to the prosthesis. The second fluid is removed such that a quantity of fluid remains within the well. The second fluid is used to expand the size and volume of the pore. After achieving the desired pore profile, the second fluid is removed and the prosthesis is rinsed in a third fluid to remove the protective coating on the surface of the prosthesis.
In accordance to another embodiment, an alternative method of forming pores on an implantable prosthesis is disclosed. The method includes applying a first fluid onto the prosthesis so that the first fluid forms a protective coating on the surface of the prosthesis. A laser is used to selectively ablate portions of the protective coating. In general, the laser drills into the prosthesis and forms one or more wells. A second fluid is applied to the prosthesis, causing the well or pore size and volume to expand. After achieving the desired pore profile, the second fluid is removed and the prosthesis is rinsed in a third fluid to remove the protective coating on the surface of the prosthesis.